1. Field of the Invention
The present invention relates to an optical disk device and a data recording method. More specifically, the present invention relates to an optical disk device and a data recording method for recording data to a disk.
2. Background Information
With an optical disk device that records data to a DVD (Digital Versatile Disk), a CD (Compact Disk) or other such optical disk (hereinafter referred to as a “disk”), an optimal laser power for the disk is determined by taking advantage of a fact that asymmetry in a recorded portion formed on the disk varies with a laser power of an optical pickup that emits laser light to the disk.
However, due to a non-uniformity of reflective film layers of the disk and so forth, it is generally difficult to uniformly maintain sensitivity characteristics of the disk to the laser light. In particular, the sensitivity characteristics of the disk tend to fluctuate in a peripheral direction of the disk.
In view of this, an ROPC (Running Optimum Power Control) is performed to maintain recording quality. In the ROPC, the laser power of the optical pickup is controlled during recording to the disk to deal with a fluctuation in the sensitivity characteristics of the disk and changes in ambient temperature.
Also, an ALPC (Automatic Laser Power Control) is performed to minimize a fluctuation of the laser power due to changes in temperature of a laser light source of the optical pickup. In the ALPC, the laser power during recording is controlled so as to match a specific target value.
Meanwhile, an axial runout slightly occurs in the disk due to deterioration with age or a usage environment after manufacturing, problems during manufacturing and so forth. When the ROPC is performed during recording data to the disk with the axial runout, the axial runout of the disk causes focal deviation to fluctuate periodically. As a result, a fluctuation amplitude appears in a peak value of an RF signal outputted from the optical pickup during recording.
FIG. 7 is a graph of relationship between the ROPC response frequency band, the ALPC response frequency band and the axial runout frequency band. As can be seen from the graph, the ROPC and the ALPC response frequency bands are different from the axial runout frequency band. Therefore, even if the ROPC and the ALPC are performed, an effect of a state change in disk radius direction or a laser temperature change is eliminated. However, an effect of the axial runout of the disk is difficult to be eliminated. Specifically, it is difficult to distinguish measured fluctuations in the RF signal peak value due to the axial runout and measured fluctuations in the RF signal peak value due to the recording quality.
Therefore, if the ROPC is performed using the peak value of the RF signal having the fluctuation amplitude due to the axial runout, the measured fluctuations in the peak value cause laser power fluctuations during the ROPC. As a result, stable control is prevented.
Also, averaging process is necessary to stabilize the measured fluctuations in the peak value of the RF signal due to the axial runout. However, because the fluctuations due to the axial runout occur in a rotational period of the disk, measurement for at least one rotational period is necessary for the averaging process. Consequently, a large amount of test recording area on an inner periphery of the disk is required.
Various techniques have therefore been proposed for correcting the effect of the axial runout.
With a conventional device, an axial runout is detected by detecting a level of a focus drive signal (see Japanese Laid-Open Patent Application No. 2005-174410, for example). Specifically, a voltage level of the focus drive signal is measured by a voltage measurement circuit. The maximum and minimum values of the voltage level of the focus drive signal are updated, and the maximum amplitude of the focus drive signal is computed by a microcomputer. Then, the computed maximum amplitude is compared to a preset reference value. If the computed maximum amplitude is greater than the reference value, then it is determined that there is an axial runout. Then, a rotation of a spindle motor is controlled, the rotational speed of the disk is controlled, and the maximum reproduction speed is limited. With the conventional device, whether or not there is any axial runout in the disk is merely determined by detecting the level of the focus drive signal. However, the effect of axial runout is not directly eliminated.
With another conventional device, a mechanism for tilt adjustment in a radial direction is driven by a focus drive signal and an offset addition signal, and a mechanism for tilt adjustment in a tangential direction is driven by a differential signal of the focus drive signal (see Japanese Laid-Open Patent Application No. 2002-358679, for example). Specifically, an axial runout of a disk is corrected by driving a tilt adjustment mechanism based on the focus drive signal. However, an effect of axial runout that appears in a peak value of an RF signal is not directly eliminated.
With another conventional device, a drive control of a mechanism for tilt adjustment of an optical pickup is performed so that a detected distance based on a focus drive signal is equal to a reference distance (see Japanese Laid-Open Patent Application No. H11-110770, for example). However, an effect of axial runout that appears in a peak value of an RF signal is not directly eliminated.
With another conventional device, for correcting an axial runout of a disk, another ALPC system that matches the frequency of the axial runout is installed in addition to an original ALPC system (see Japanese Laid-Open Patent Application 2004-171768, for example). However, with this conventional device, a hardware modification (a modification to an internal part of an integrated circuit) is necessary, which increases a manufacturing cost.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved optical disk device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.